feat(config): shared app.properties for app-wide constants

Add a single source of truth (root app.properties) for public app-wide
constants, injected at build time on both platforms instead of hardcoding.

- Apple: generate-appconfig.sh -> Generated/AppConfig.swift (wired into
  `make apple-app-config`), consumed as AppConfig.privacyPolicyURL.
- KMP: generateAppConfig task -> AppConfig.kt (mirrors DiagnosticsBuildConfig),
  consumed as AppConfig.PRIVACY_POLICY_URL.

Replaces the stale hardcoded privacy-policy URL on both sides with
https://vnidrop.sudosy.fr/privacy/.

Also fix the Apple release core build: disable release LTO in build-core.sh
(Cargo forbids lto in a build-override) to avoid the proc-macro
"mis-aligned LINKEDIT string pool" corruption, so release archives are
compact instead of shipping the debug core.

Update the app icon.

Tests: shell test for the generator (escaping, missing/duplicate key),
plus XCTest and jvmTest asserting the generated value matches app.properties.

shared/src/commonMain/kotlin/com/vnidrop/app/feature/settings/AboutSettings.kt

@@ -52,7 +52,7 @@ import vnidrop.shared.generated.resources.os_version_title
 import vnidrop.shared.generated.resources.value_unavailable
 import vnidrop.shared.generated.resources.version_title
 
-private const val PrivacyPolicyUrl = "https://github.com/vnidrop/vnidrop"
+private val PrivacyPolicyUrl = com.vnidrop.app.AppConfig.PRIVACY_POLICY_URL
 
 @Composable
 internal fun AboutSettings(

shared/src/jvmTest/kotlin/com/vnidrop/app/AppConfigTest.kt

@@ -0,0 +1,40 @@
+package com.vnidrop.app
+
+import java.io.File
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+/**
+ * Verifies the build-time [AppConfig] (generated from the shared `app.properties`)
+ * exposes the expected, well-formed values to the shared UI.
+ */
+class AppConfigTest {
+	@Test
+	fun privacyPolicyUrlIsTheExpectedHttpsEndpoint() {
+		assertTrue(AppConfig.PRIVACY_POLICY_URL.startsWith("https://"), "must be https")
+		assertEquals("https://vnidrop.sudosy.fr/privacy/", AppConfig.PRIVACY_POLICY_URL)
+	}
+
+	@Test
+	fun privacyPolicyUrlMatchesTheSharedConfigFile() {
+		// Cross-check the generated constant against the single source of truth so a
+		// broken codegen (or drift) is caught, not just a hardcoded copy.
+		assertEquals(privacyUrlFromAppProperties(), AppConfig.PRIVACY_POLICY_URL)
+	}
+
+	private fun privacyUrlFromAppProperties(): String {
+		var dir: File? = File(System.getProperty("user.dir")).absoluteFile
+		repeat(8) {
+			val candidate = File(dir, "app.properties")
+			if (candidate.isFile) {
+				return candidate.readLines()
+					.firstOrNull { it.startsWith("PRIVACY_POLICY_URL=") }
+					?.substringAfter("PRIVACY_POLICY_URL=")
+					?: error("PRIVACY_POLICY_URL missing in ${candidate.path}")
+			}
+			dir = dir?.parentFile
+		}
+		error("app.properties not found from ${System.getProperty("user.dir")}")
+	}
+}